Pathogenicity of H7N7/ 03 viruses in ferrets. Ferrets were inoculated i.n. with 107.4 TCID50 of either maH7N7 or chH7N7 virus. As negative control, one group of ferrets was mock-infected. On day 5 p.i., 3 of the 7 animals per group were euthanized for post mortem examination. The remaining animals were monitored for clinical signs and body weight changes during 14 days p.i. A) Median scores for lethargy. B) Median scores for sneezing (if a ferret was euthanized, the last assigned score was carried forward). C) Kaplan-Meier survival curves. D) Mean body weight changes relative to baseline weights at day 0. Only 2 ferrets of the maH7N7 group remained on day 13 p.i. Error bars represent standard deviations. E, F) Semi-quantitative scoring of histopathological changes in lung tissues. Microscopic lung changes were scored on a scale of 0 to 5 as detailed in the Methods section. Each point represents the histology score of an individual animal and horizontal bars represent the median group scores. Lungs were examined E) on day 5 and F) on day 14 p.i. or when an animal needed to be euthanized before the end of the study period (one on day 11 and 12 each, shown with open circles).